Strandloper
by Fiachra15
Summary: "All in all, the day John's perception of the world turned upside down began in an ordinary fashion." Sherlock is...different. Unique. Almost a legend in his own right. But John could never have imagined just how appropriate that last description would turn out to be... Or: In which Sherlock is a bit not human and John deals with it remarkably well most of the time.
1. Of Fish, Detectives and Something In-Bet

**I don't know who came up with this AU. It's nuts. But it's imaginative and I love it. So here is the first Sherlock story I started writing (after many rewrites) split into oneshot format for your enjoyment (hopefully).**

 **One of my motivations for writing this was the lack of stories in this AU that didn't revolve around smut or slash. So here is a platonic merlock story, no slash, no smut and no kinks. And with the minimum of crackiness. (However if you really want to read this with your shipper goggles on, go ahead.)**

 **1: Of Fish, Detectives and Something In-between**

 _"I must be a mermaid, Rango. I have no fear of depths and a great fear of shallow living."_

-Anaïs Nin

David Miller sighed with relief as he exited the office building in Canary Wharf. It had been a long and stressful day, filled with two meetings, several conference calls and angry words with his incompetent intern. He was delighted at finally being able to return home. It was a bitterly cold evening and the icy breeze caused murky clouds to whisk across the rapidly darkening sky. Gripping his briefcase, he turned his collar up against the wind and set off at a brisk pace towards the Tube station. A splash caused him to pause and turn his attention to the docks. Tiny wind-whipped crests chased each other across the surface, illuminated by the orange street lamps, and lapped gently against the concrete bank. The sound he had heard had been louder than that. Intrigued, he moved nearer, peering into the gathering gloom, for the street lights didn't reveal all of the dark water. Suddenly what appeared to be the fin of an enormous fish broke the surface along with the faintest glimmer of scales before vanishing as quickly as it had appeared. David blinked rapidly and rubbed his eyes. He waited for a few minutes, shivering when the wind picked up but it was gone, whatever it was, and so he turned and hurried towards his original destination, making a mental note to avoid working so late in the future. From the shadows between the watery orange reflections of the lamps a pair of pale blue eyes watched him disappear from view, before sinking silently below the water's surface.

oOo

"John, get up we have a case!"

"Wha-"

But Sherlock had bounced out of sight before John could tell him off for coming into his room without permission. John sighed, got dressed, tried to take in Sherlock's excited summary of what had happened on the taxi ride to the scene and tried not to dwell too much on the fact that everyone they passed seemed to be eating food of some sort while he definitely was not. All in all, the day John's perception of the world turned upside down began in an ordinary fashion.

As the cab pulled up to a nice row of houses in Kensington, John had woken up sufficiently to pluck up the courage to ask Sherlock to repeat himself. Sherlock sighed irritably but complied as they strode past other Yard officials and up the stairs to the first floor.

"Locked room mystery. No apparent signs of murder or suicide, according to the victim's wife, but then again, what does she know?" They were standing at the flat's door at this stage, and a hassled looking Lestrade let them in.

The first impression John got was one of wealth. The flat was spacious and decked out in modern, expensive looking furniture. It was a bit too bland for John's taste, nearly everything was in shades of white or cream, as if it had being designed specifically to be featured in a magazine of modern homes. The only splash of colour came from a large fish tank that served as a divider between the kitchen, which was heaving with every appliance under the sun, and the living room, which they were standing in. The wife, who like the rest of the flat was dressed expensively from head to toe and had dark tracks of eyeliner running down her face, was sobbing noisily to Donovan, who did not look impressed at all.

"He used to listen to loud music whenever I was out! That's why he always locked the door, because he could never hear anyone coming!" she wailed while Donovan tried not to wince from the shrill voice she was been forced to endure at such close range.

"Unfortunate for him, what do you think? Sherlock?" John frowned. Sherlock was staring at the tank, a faraway look on his face. "Sherlock? You okay?"

"Yeah, fine." He said distractedly before drifting over to the aquarium. John followed, amazed when Sherlock ignored the body in front of the tank and peered into it. Lestrade gave John a puzzled look, who shrugged in response. It was impressive, even from someone who knew nothing about fishkeeping. About four feet long, it was stocked with a shoal of large yellow fish, which seemed to be regarding Sherlock curiously, corals and some other fish in myriad colours.

John shook his head and knelt beside the prone corpse and began his quick examination. He looked up as Greg joined him. "Well, there's nasty puncture wound and swelling on his hand, it doesn't look suspicious but…" He shook his head. "Sherlock, do you not want to have a look? Sherlock!" Sherlock whirled around, blinked and looked down at John.

"What?"

John looked at him incredulously. "Body. Don't you want to examine it?"

Sherlock ignored him and turned to the dead man's wife, John noticed that the yellow fish (what _were_ they called?) seemed to be watching Sherlock's movements intently. "How long has he had the tank?"

"I'm sorry?" She asked in confusion, wide eyes staring at him from her mascara-smudged face. Sherlock sighed theatrically. "The fish tank! How long had your husband had it?"

."About a month, he got the suppliers to get everything ready for him, so he could start straight away-" Sherlock motioned her to be quiet and looked back at the body.

"Well? What happened?"

"You saw the swelling on his hand, didn't you?"

"Yes, but-"

"As ever, you see but you don't observe John!"

Sherlock rolled his eyes at the blank looks on everyone's faces and launched into his usual rapid-fire deductions. "It's a new tank, saltwater, usually the realm of experienced hobbyists, which he clearly wasn't if his stocking levels are anything to go by. If any of you had taken the time to look, you would have seen that this rock had fallen, quite recently, the pale underside is exposed. It's blocking this coral's light," he pointed it out "So he tried to move it, only to get stung by something underneath the rock. Something, that if you're allergic to it, can cause heart failure and death."

"Which is?" Greg prompted.

Sherlock, only too happy to point it out, pulled off his coat, rolled up his shirt sleeve and plunged his hand into the tank, much to everyone's protests. Gently swatting the yellow fish aside, who seemed delighted that Sherlock was sharing their space, he carefully lifted a piece of rock and withdraw his arm quickly. John and the others crowded around him. As the sand settled, they saw a large, grumpy-looking red and white striped fish flare its enormous fins aggressively at them.

" _Pterois volitans_ , the Volitans lionfish." Sherlock said. "Hardy, not usually deadly, but still not the best fish for a novice. I suggest you class his manner of death as accidental once the autopsy report shows I'm right and arrange for his livestock to be rehomed, preferably to more responsible owners. Keep the tangs together though, they seem to like each other's company." He replaced the rock, scowling at the lionfish as it spread its fins towards him and rubbed his arm dry with an offered towel.

"Well, um, thanks. You can go if you want." Greg said to John, who nodded.

"Ready Sherlock?"

Sherlock looked away from the tank and blinked at him. "Sorry?"

"You solved the case, we can go?" said John slowly, as if Sherlock had forgotten what usually happened on cases.

"Yes, of course." Sherlock said, seemingly back to normal. "Give me the details of whoever you call to deal with the fish." He said to Greg as he headed to the door, who nodded in confusion. John followed, after giving the yellow fish an odd look, they looked like they were sadly watching Sherlock leave, like spurned puppies.

"So I guess you could say that case was a bit "fishy"." John heard Anderson say as he shut the door behind him.

"Shut up Anderson!" and groans were the resounding answer.

oOo

"So how did you know all that?" John asked in the cab home.

"Know all what?" Sherlock said coyly.

"About the fish and fishkeeping. I know it was venomous and that's probably relevant information to you, but you usually never show much interest in animals."

"I like marine animals." Answered Sherlock nonchalantly, gazing out of the window.

"Really? I never knew."

"There's a lot you don't know about me John." Was the soft reply.

John was about to make a sarcastic comment about that not being the case if Sherlock would only talk about himself more, but stopped when he saw Sherlock's expression. He was looking out the window with an odd look on his face, similar to what he looked like when he saw the fish. He looked, sad, as if he was longing for something.

John turned to look out his own window, thinking. Sherlock was acting odd (well, odd _er_ ), to be more captivated by ornamental fish than a corpse? And now to stare out of the window like some wistful lover in an old film? What was with him today? John was baffled.

Sherlock was quiet when they walked up the stairs to the flat. He hadn't spoken a word since the beginning of the cab ride. The solemn silence was starting to worry John, and just as he opened his mouth to ask what on Earth was the matter with him when he shut the door behind them, Sherlock said, "I'm taking a bath."

"Um, okay?" John said as Sherlock vanished down the hall. "Are you alright?" Sherlock never usually announced when he wanted to use the bathroom for something, which had led to some sights over the years that John could have gone his entire life without seeing.

"I'm fine." Came Sherlock's muffled reply before the door banged shut.

oOo

When John returned about an hour later from a walk and the shop, 221B was oddly quiet. Too quiet. He frowned as he placed the shopping bags on the table. Sherlock's coat was still hanging up, and his phone was next to his microscope, so he hadn't gone out. His bedroom door was open and he wasn't in there either. So if he wasn't in his room, or in the rest of the flat and he hadn't gone out…. John looked at the bathroom door, which was still shut. Really? After this length of time? He stepped forward, and hesitated. This was Sherlock, he was probably fine. But then again… He tapped lightly on the door. "Sherlock? Sherlock? Are you in there?"

No answer.

Feeling a bit apprehensive now, John tried the handle. Locked, of course. Moving into Sherlock's room, he knocked again. "Sherlock, I'm coming in." At the lack of response, he pushed open the door and entered the bathroom.

And then proceeded to let out a high-pitched shriek of, "Jesus Christ!"

Sherlock awoke and jumped, sloshing water over the side of the bath. "John!" he yelped in surprise, "I can explain…" At that moment, Mrs. Hudson's voice reached them from downstairs, "Are you two alright?"

"We're fine." John managed to call back, shutting the door behind him and sliding down it to sit on the tiled floor.

"Are you? You don't look it." Sherlock said in concern.

"I'm…" John looked at Sherlock's legs, only they weren't, they were scaly, and… "Actually, I'm not sure if I am…"

"Don't pass out. Just, shut your eyes and breathe."

John did, and concentrated on breathing in and out. He could hear Sherlock shift in the bath, but otherwise remain quiet. After a minute, John opened his eyes, gingerly stood up, moved closer to Sherlock and knelt next to the bath, Sherlock watching him warily. "Is that…are you…" John swallowed "are you a…a mermaid?"

Sherlock sighed. "I'm male, John, in case you hadn't noticed." But then he softened slightly. "But yes, I suppose "merman" would be an appropriate term."

"How?" John stared unabashedly at the gleaming, fish-like tail that had replaced his friend's legs. "This isn't a trick is it? You didn't spike my tea did you?" He pinched his arm, and winced. Not a dream either then.

"This isn't a trick, nor did I spike your tea." Sherlock huffed in indignation at the thought. "As to how…" he shrugged. "There was an old story on my mother's side of the family that one of her ancestors was a mermaid, and ever since then they had a particular affinity with the sea. Well, it was just a story until Mycroft and I were born." He flicked his tail, drawing John's attention to it again.

It began at his hips, pale skin transitioning smoothly and seamlessly to scales, and added to Sherlock's height by about two feet at the most and tapered to an elegantly curved caudal fin. Noticing John's interest, Sherlock turned on his side, exposing a spiky dorsal fin that ran from the centre of his shoulder blades to the small of his back. The colour of his tail was not unlike that of a mackerel, except without the black stripes. Darkest on top, it gradually paled to cream on his underside. More scales extended from his tail and continued up his spine, clustering around the base of his dorsal fin, terminating at the base of his skull. He rolled on to his back again, causing a silver shimmer to run along his tail. "You can touch, if that helps."

"Really?"

Sherlock nodded, light glinting off small, lightly coloured blue-green scales on his cheekbones. Similar ones were scattered along his forearms, and when he waved a hand in his tail's direction, translucent webbing connected his fingers. John cautiously rolled up his sleeve and laid his hand on Sherlock's tail. To his pleasant surprise, it wasn't slimly like some fish he remembered catching as a kid. Instead it was smooth and seemed to be packed with muscle. He ran his hand down towards the fin, eyes wide in wonder.

"That's…amazing."

Sherlock's mouth quirked up in a smile. "Convinced it's real now?" John nodded.

"Good, I thought you were going to faint for a moment when you came in."

"To be fair, you turning out to be half fish isn't exactly something I was expecting to see."

"I'm not half fish," Sherlock said indignantly, "I'm half Mer."

"Mer?"

"Merfolk, merpeople, finfolk, dinny mara, aipalookvik, merrymaids, sea-morgans, merrows, take your pick. I think "Mer" sounds good though, dignified."

"Of course you would," John snorted, "I'm sorry about barging in on you, I thought something was wrong."

"It's fine." Sherlock said. "Not the way I originally planned on telling you, but it was effective." John blinked. "You were going to tell me?"

"Of course. " _"Potential flatmates should know the worst about each other"_ ," he recited, "Friends even more so." John flushed at the unexpected sentiment. "Why are you in here anyway?"

"Becoming Mer is like an itch I need to scratch every now and then, and it's nicer to do it in water. There's too much of a risk during daylight to use the Thames, and I couldn't wait until night. This is warmer anyway." John nodded and sat back on his heels. "Okay, so this is really, really odd, but as long as you don't try to drown me or anything, it doesn't bother me."

Sherlock narrowed his eyes, seeming to scan John in order to prove the validity of his statement. "Really? It doesn't bother you at all?" John shrugged. "Why should it? You can grow a tail, it might take me a while to get my head around that, but it's fine."

Sherlock looked momentarily baffled, then smiled. "Thank you. Oh, and John?" he said as John started to leave, "Merpeople don't usually drown soldiers, so you'll be fine. If you were in the Navy on the other hand…" He grinned mischievously.

John's expression, from Sherlock's point of view, was priceless.


	2. So Long, and Thanks for all the Fish

_**2: So Long, and Thanks for all the Fish**_

 _The fish and I were both stunned and disbelieving to find ourselves connected by a line."_

\- William Humphrey in "The Armchair Angler"

Fish.

The flat was full of fish. Yellow fish swimming in an impressive variety of containers that were perched on nearly every available surface. Sherlock (of course this was his doing) had scavenged a few small aquariums from goodness knows where but the majority of their new flatmates were in buckets, plastic storage crates and one specimen was floating contently in what looked suspiciously like one of Mrs. Hudson's larger Tubberware containers. John turned in a circle, bewildered and just thankful that they were living fish, unlike some of the things Sherlock brought back for "experimental purposes".

"Sherlock, I know I said I was fine with you being, you know, but isn't this a bit much?"

Sherlock poked his head out of the kitchen. "They're from yesterday's case. Graham couldn't find anywhere that could take all of them at such short notice and the aquarium can't take them for another two days so I said I'd hold on to them until they were ready for them."

"It's Greg." John tried to correct him in vain, "Why couldn't they just stay in the flat?"

"The falling rock had cracked the glass, they thought it better to remove all the animals as soon as possible. They found shops that would take the others but no one had the capacity or wanted to keep all the tangs together."

John, keeping his observation that _they_ barely had space to himself, knelt down beside the largest crate to look at them more closely. "If you were taking in homeless fish I would have thought you'd have taken the murderous lionfish, he seemed more like your ideal pet."

Sherlock came over to join him, the tangs flocking to his side of the crate when he sat cross legged on the floor. "Murderous isn't a very accurate description John, animals don't plan their kills the way humans do. It was a female actually, and not the nicest. Appalling language and temper, worse than you on a bad day."

"I'm not that bad-wait," John stared at Sherlock in realisation. "you can talk to fish."

"Yes, I would have thought that was obvious from how I solved that case."

John just kept looking at him incredulously. "You can talk to fish." He repeated.

"Yes, we've established that." Sherlock raised an eyebrow. "I suppose now is a good time to tell you that I can communicate with aquatic animals?"

John laughed in part disbelief, part child-like wonder.

"Dolphins?"

"Yes."

"Seabirds?"

Sherlock hummed in affirmation.

"Seals?"

"Yes, and I'm going to stop you there."

John looked back at the tangs, which were still milling around at Sherlock's side. "What are they saying?"

"They don't speak in the same way we do," Sherlock explained, "They use colour and gestures to communicate, and that translates into meaning. For me anyway. More vocal animals are easier to talk to, because it's just like learning a human language. Sort of. As for what they're saying…" he watched them for a moment "It's not much. They're just excited to be able to speak to me, and to be able to live with me for a while. Humans, or half-humans, that can understand animals aren't commonplace you know."

John watched the tangs with a touch of pity now, this was probably the most exciting thing that had happened to them in a while. "How did they help you solve the case?"

"They told me what happened, and where to look for the lionfish. They're not as stupid as people think."

"Can they understand me?"

"No, just me."

"Ah."

John was about to get up, but then Sherlock opened his mouth. The sound that came out was unlike anything John had ever heard. It was fluid and musical, almost as if the language was sung instead of spoken. Interspersed within it were some noises John thought he recognised, such as clicks and a whistle that sounded like something a dolphin would make. The tangs suddenly swarmed to the side of the crate nearest John and watched him, waving their fins to stay in position. John stared in Sherlock's direction, who smiled at the look of wonderment that must have been on his face.

"I introduced you, and they now find you fascinating because of your connection with me. I tried to tell them that you were a surgeon, since they're surgeon fish, but I don't think they understood that bit."

John didn't really know what to say. "Can you tell them thanks?"

Sherlock grinned and clicked a few times, the tangs bobbed in response. "I didn't learn to speak Mer, like everything else it seems to be a built in ability." He put his hand in to the water and let the tangs cluster around it, nuzzling his fingers affectionately.

"You should have been a marine biologist."

Sherlock's lips tightened and a strange, almost sad, look flitted momentarily across his face. "It would have been too tempting." He murmured, still looking forlorn and lost, as if in a memory. He shook himself and blinked, back to normal. "You can put your hand in too."

It took a bit more encouragement, but John allowed the fish to investigate his hand while Sherlock told him about the animals he had spoken with, whatever John's question had awoken forgotten by the two of them, at least for now. John laughed when Sherlock told him about Mycroft using gulls to keep an eye on the Thames area for him, he couldn't imagine Mycroft in his fancy suits chatting to a flock of gulls.

"So if Baker Street starts to look like a scene from _The Birds_ , I should blame Mycroft."

"Exactly. But the good thing is that some of the gulls like me, so with a bit of persuasion I can, _encourage_ , them to annoy him. I asked them to bother him as he was going to a meeting once. You should have seen his face, and the state of his suit."

John shook with mirth, causing the tangs to scatter.

oOo

It was certainly an odd two days, but finally the fish had to go. John didn't know who was more morose when Sherlock's contact from the London Aquarium came to pick them up, Sherlock or the tangs. They hovered at the side of their respective containers staring at Sherlock, there was no other way to describe it, accusingly, and deliberately made their transferal to the containers in which they would make their way to the aquarium more difficult than necessary until Sherlock discreetly wiggled his fingers at them (John assumed he was mimicking their fin movements).

John helped carry the lidded buckets down to the van, being even more conscious of his cargo than he would have been before this madness had started. "He used to help us out you know." Tim, the aquarium employee, told John. "Before he started detecting, and before he got too busy. Anything that involved handling the animals in some way, catching them, vet visits and things like that. They just completely relaxed around him. We had awful trouble with one of the penguins the other day, I should have called him but I completely forgot. I wasn't sure if he'd come anyway."

"You should," John said, suddenly confident that he was speaking the truth, "He would love to, I know he would."

Tim grinned broadly and shook John's hand heartily, then turned as Sherlock helped Laura (Tim's co-worker) place the last few containers into the back of the van. "John was just saying that you'd like to come and help us again, if you have time." Tim said cheerfully before John could stop him. Sherlock looked from Tim to John and back again.

"I'd…yes, I would, actually." He said haltingly as Tim pumped both their hands up and down enthusiastically and drove away with a shout of, "So long, and thanks for all the fish!" which he seemed to find hilarious. John waited until the van was gone before turning to Sherlock, "I'm sorry, he told me about what you used to do with them and how he wished he had had your help with a penguin the other day, and I just blurted it out."

"No, it's fine." Sherlock said, and surprised John with a genuine smile, "I keep meaning to say it to them but I always forget."

"You mean you're too proud to, you plonker. At least that's cheered you up, I thought that I'd have to buy you a goldfish to keep you happy."

"I never had a goldfish when I was younger, or even at university, I could barely take care of myself, I didn't want to endanger another life too."

"You know that that's what people usually say when they say that they don't want kids." John said as they headed up the stairs.

"Goldfish are much more interesting. Did you know that their memory lasts for three months? Why was Tim so absurdly happy when he made that last statement? He was thanking us for minding the fish, what was so funny?" Sherlock said, confused, as he sat at the desk and opened a laptop.

"Douglas Adams reference. _The Hitchhiker's Guide to The Galaxy_? Never mind. What are you looking up?"

"Aquariums."

"I'm not getting you a fish Sherlock, you heard Tim, you can go to help them out whenever you want." Sherlock scowled and then began typing furiously with a grin that set off John's internal "Sherlock is about to do something stupid" alarm bells. "What are you doing? Is that my laptop?"

"I'm updating your post about babysitting a shoal of fish by saying that you are now refusing to get me one."

"Sherlock!"

 **Sorry for the long wait, life kept throwing up things that had to be dealt with**.


End file.
